The present invention relates generally to an apparatus for checking the functionality of a fuel tank vapor pressure sensor using vacuum produced by a pump at an atmospheric port.
A non-integrated vehicle fuel system includes a normally-sealed fuel tank. Fuel system integrity is verified by the presence of pressure or vacuum created by temperature difference or a leak check pump. If the system holds pressure or vacuum above a certain threshold, the fuel system is considered leak free.
Because the fuel system integrity determination relies upon the tank vapor pressure sensor reading, a rationality check must be performed on the fuel tank vapor pressure sensor. Primary failure modes such as sensor-offset or sensor-stuck-in-range must be checked.
The architecture of a non-integrated fuel system presents unique challenges to verify leak integrity without redundant pressure sensors or excessive emissions. For example, in order to reliably ensure that the indicated fuel tank vapor pressure is correct, the fuel system might, for example, include two pressure sensors and compare the outputs of the sensors. If a difference in output from the sensors is present, the system's diagnostics sets a malfunction indicator warning light. But this technique requires a second sensor, a manifold, and a hose connecting the manifold to a carbon canister.
A need exists for a fuel system and method for checking that the vapor pressure sensor returns to zero and is not stuck-in-range without actually relieving all the pressure or vacuum in the fuel tank. Performance of the system should comply with emission regulations at low cost.